Messages in this thread | | | Date | Wed, 16 Nov 2022 14:24:48 -0800 | From | Deepak Gupta <> | Subject | Re: [PATCH v5] scripts/gdb: add lx_current support for riscv |
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On Wed, Nov 16, 2022 at 09:16:49AM +0100, Andrew Jones wrote: >On Tue, Nov 15, 2022 at 02:10:51PM -0800, Deepak Gupta wrote: >> csr_sscratch CSR holds current task_struct address when hart is in >> user space. Trap handler on entry spills csr_sscratch into "tp" (x2) >> register and zeroes out csr_sscratch CSR. Trap handler on exit reloads >> "tp" with expected user mode value and place current task_struct address >> again in csr_sscratch CSR. >> >> This patch assumes "tp" is pointing to task_struct. If value in >> csr_sscratch is numerically greater than "tp" then it assumes csr_sscratch >> is correct address of current task_struct. This logic holds when >> - hart is in user space, "tp" will be less than csr_sscratch. >> - hart is in kernel space but not in trap handler, "tp" will be more >> than csr_sscratch (csr_sscratch being equal to 0). >> - hart is executing trap handler >> - "tp" is still pointing to user mode but csr_sscratch contains >> ptr to task_struct. Thus numerically higher. >> - "tp" is pointing to task_struct but csr_sscratch now contains >> either 0 or numerically smaller value (transiently holds >> user mode tp) >> >> Patch also adds new cached type "ulong" in scripts/gdb/linux/utils.py >> >> Signed-off-by: Deepak Gupta <debug@rivosinc.com> >> Reviewed-by: Andrew Jones <ajones@ventanamicro.com> >> >> --- >> Since patch has changed a little bit from v1 and I didn't include >> changelog earlier, here it is. >> >> v1 --> v2: >> - added logic to locate task_struct irrespective of priv >> - made locating task_struct agnostic to bitness(32 vs 64). >> - added caching of ulong type in scripts/gdb/linux/utils.py >> - added more descriptive commit message >> >> v2 --> v3: >> - amended commit message and source line to fit column width >> >> v3 --> v4: >> - amended commit message and remove whitespace in source >> - added Reviewed-by for reviewers >> >> v4 --> v5: >> - changing the order of changelog and sign off/review tags in commit >> --- >> --- > >Everything looks good, but you've got extra ---'s here. They don't hurt, >but if you're still ironing out your workflow you may want to keep in >mind that you don't need them. You only need one, which goes above the >changelog. > >Thanks, >drew >
Noted. Thanks.
>> scripts/gdb/linux/cpus.py | 15 +++++++++++++++ >> scripts/gdb/linux/utils.py | 5 +++++ >> 2 files changed, 20 insertions(+) >> >> diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py >> index 15fc4626d236..14c22f82449b 100644 >> --- a/scripts/gdb/linux/cpus.py >> +++ b/scripts/gdb/linux/cpus.py >> @@ -173,6 +173,21 @@ def get_current_task(cpu): >> else: >> raise gdb.GdbError("Sorry, obtaining the current task is not allowed " >> "while running in userspace(EL0)") >> + elif utils.is_target_arch("riscv"): >> + current_tp = gdb.parse_and_eval("$tp") >> + scratch_reg = gdb.parse_and_eval("$sscratch") >> + >> + # by default tp points to current task >> + current_task = current_tp.cast(task_ptr_type) >> + >> + # scratch register is set 0 in trap handler after entering kernel. >> + # When hart is in user mode, scratch register is pointing to task_struct. >> + # and tp is used by user mode. So when scratch register holds larger value >> + # (negative address as ulong is larger value) than tp, then use scratch register. >> + if (scratch_reg.cast(utils.get_ulong_type()) > current_tp.cast(utils.get_ulong_type())): >> + current_task = scratch_reg.cast(task_ptr_type) >> + >> + return current_task.dereference() >> else: >> raise gdb.GdbError("Sorry, obtaining the current task is not yet " >> "supported with this arch") >> diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py >> index 1553f68716cc..ddaf3089170d 100644 >> --- a/scripts/gdb/linux/utils.py >> +++ b/scripts/gdb/linux/utils.py >> @@ -35,12 +35,17 @@ class CachedType: >> >> >> long_type = CachedType("long") >> +ulong_type = CachedType("ulong") >> atomic_long_type = CachedType("atomic_long_t") >> >> def get_long_type(): >> global long_type >> return long_type.get_type() >> >> +def get_ulong_type(): >> + global ulong_type >> + return ulong_type.get_type() >> + >> def offset_of(typeobj, field): >> element = gdb.Value(0).cast(typeobj) >> return int(str(element[field].address).split()[0], 16) >> -- >> 2.25.1 >>
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